Problem: Simplify to lowest terms. $\dfrac{55}{99}$
Answer: What is the greatest common factor (GCD) of 55 and 99? $55 = 5\cdot11$ $99 = 3\cdot3\cdot11$ $\mbox{GCD}(55, 99) = 11$ $\dfrac{55}{99} = \dfrac{5 \cdot 11}{ 9\cdot 11}$ $\hphantom{\dfrac{55}{99}} = \dfrac{5}{9} \cdot \dfrac{11}{11}$ $\hphantom{\dfrac{55}{99}} = \dfrac{5}{9} \cdot 1$ $\hphantom{\dfrac{55}{99}} = \dfrac{5}{9}$